1. Field of the Invention
The present invention relates in general terms to brakes with axially expanding brake shoes, that is to say brakes of the kind which comprise a rotating member possessing a peripheral annular groove, the opposite radially extending faces of which form two braking surfaces, and at least one actuating block radially engaged in the said groove and connected to support means, the said actuating block comprising, for each braking surface, at least one actuating unit suitable for applying a brake shoe against the braking surface.
Such brakes with axial expansion are useful particularly in cases where high-energy braking is necessary, whether this be for ground gear, such as a winding drum or cable drum, or for a vehicle, such as a railway vehicle or a heavy road vehicle.
The present invention relates, in particular, to those brakes with axially expanding brake shoes in which each actuating unit comprises a cylinder, which is open at both its ends, and two pistons, which are mounted so as to move in opposite directions in the said cylinder, the said cylinder and the said pistons defining a fluid chamber interconnected to a feed nozzle suitable for connection to a pressurized fluid source.
2. Discussion of the Prior Art
Such a brake is described, for example, in U.S. Pat. No. 2,957,552.
In this American patent, the actuating block employed is bulky, the cylinders of the actuating units which it comprises being directly formed by bores in this block, and the axial thickness of the latter being substantially equal to the axial length of these cylinders.
This results in a relatively heavy and hence expensive construction.
In contrast, the French Pat. No. 2,188,732 has already proposed a relatively light construction, in which the actuating block is formed of two thin plates which are set up parallel to one another and separated from one another, these plates being strutted at certain places by means of tubes which form cylinders.
Thus, between such tubes, the two plates are separated from one another by an open space.
However, in practice, a construction of this type involves welding which, because of the heating resulting therefrom, lead to deformation and in particular to ovalisation of the cylinders.
Moreover, although such deformation is in fact mechanically acceptable, a construction of this type, with welds, cannot easily be manufactured by a process which is other than small-scale, and the characteristics which can thereby be achieved therefore will be considerably non-uniform.